The present invention relates generally to two-barrel carburetors, and specifically it relates to a closed loop air-fuel mixture control system employing such carburetors.
The concept of closed loop air-fuel mixture control is known as an effective means for controlling air-fuel mixture at the stoichiometric air-fuel ratio. In the closed loop control, a zirconium dioxide sensor is usually employed as a means for detecting the oxygen concentration of the exhaust emissions as a measure of air-fuel ratio at the entry to a three-way catalytic convertor which works at the maximum efficiency when the air-fuel ratio is at the stoichiometric value. The zirconium dioxide sensor delivers a signal which changes sharply in amplitude at stoichiometry, the signal being modified into a form appropriate for controlling the air-fuel metering device to adjust the mixture ratio at the stoichiometric value.
If it is desired to apply this concept to a two-barrel carburetor, separate control units may be required for the primary and secondary metering devices. Since the primary barrel supplies mixture for idling, light load and cruising at part throttle, and also for full throttle operation at low speeds, if the vehicle is operated mainly under such conditions, it would be uneconomical to provide closed loop control circuits separately to the primary and secondary metering devices.